Apparatus for rejuvenating and prolonging the life of hypo solutions



May 7, 1957 c. E. DulsENBr-:RG -ETAL 2,791,555 APPARATUS FOR REJUVENATING AND PRoLoNGING THE Filed April 11. y195s LIFE OF HYPO SOLUTIONS 2 Sheets-Sheet 1 4 m .2 w i; if

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Armen/71s May 7, 1957 c. E. DulsENBERG Erm. 2,791,555

APPARATUS FOR REJUVENATING AND PROLONGING THE LIFE 0F HYPO SOLUTIONS Filed April 1l, 1955 2 Sheets-Sheet 2 :E I E 3.

Poem/*Al EEO/foga IN1/15mm gag/w United States Pater APPARATUS FOR REJUVENATING AND PRO- LONGING THE LIFE OF HYPO SOLUTIONS Charles E. Duisenberg, Palo Alto, and Robert H. Bedford, Los Gatos, Calif.

Application April 11, 1955, Serial No. 500,438

5 Claims. (Cl. 2011-212) This invention relates generally to a method and apparatus for rejuvenating and prolonging the life of hypo solutions.

It is well known that the effectiveness of a hypo solution is reduced as the silver content is increased. In the past, apparatus has been constructed for plating out the silver. Prior apparatus was intended primarily for recovering the silver rather than prolonging the life of the hypo solution.

`The chemistry of the electrolytic separation is complex. It is believed that the deposition of silver at the cathode is a secondary reaction. The hypo salts yield sodium cations and vthiosulfate anions. The thiosulfate ions which are negatively charged migrate towards the anode and upon reaching the anode are oxidized and the free silver ions remain in the solution. At the cathode, the sodium cations `are discharged as sodium atoms and are so reactive that they decompose any ions which exist in the vicinity of the cathode. If any thiosulfate ions are present, silver is deposited on the cathode plates. If not, highly reactive sodium atoms reduce the hypo to a series of compounds, most of them fatal to the hypo solution. One of the compounds which is generally present when sufiicient thiosulfate ions are not present in the vicinity of the cathode is silver sulfide. The silver sulfide is dark brown in color and shortens the life of the hypo solution.

VIn the past, the problem was one of preventing the formation of silver sulfide and the other compounds. In order to assure a supply of thiosulfate ions in the vicinity of the cathode to thereby cause the sodium atoms to react therewith and deposit the silver on the cathode, many expedients were tried. For example, a pumping means, associated with the bath, continuously circulates the hypo solution past the cathode. 'Ihe disadvantage with such a method is that the hypo solution is very corrosive and the pumping means rapidly corrodes and deteriorates. Further, circulation past the plating surface is inadequate. Another means employed for assuring a supply of thiosulfate ions at the cathode is that of bubbling air in the solution adjacent the cathode. Although this expedient is notsubject to the above disadvantages, it nevertheless is not satisfactory, because bubbling the air through the solution does not give uniform ow of the hypo solution past the cathode and objectionable foaming results. As a consequence, there are regions of solution which are void of thiosulfate ions adjacent the cathode, and silver sulde is formed. Another proposal has been to provide paddle wheels which revolve adjacent each of the cathode plates. Again, the disadvantage with such a system is that the ow of the hypo solution past the cathode plates is not uniform and as a consequence, silver sulfide is iormed. Another disadvantage with methods in which the solution is mechanically agitated is that it has been necessary to place a bearing in contact with the hypo solution. In a short time, the bearing becomes corroded. Such machines are necessarily large and space consuming.

2,791,555 Patented May 7, 1957 prolonging the life of hypo solutions.

It is another object of the invention to provide a method and apparatus which assures a supply of thiosulfate ions in the vicinity of the cathode.

It is another object of the present invention to provide a method and apparatus in which a rapid plating rate and silver recovery may be achieved.

It is a further object of the invention to provide a method and apparatus in which there are no regions void of thiosulfate ions adjacent the cathode plates.

It is another object of the present invention to provide a method and apparatus which may be used in conjunction with existing hypo baths and which does not require additional tanks.

It is a further object of the invention to provide apparatus which does not have bearings or pumps which are in contact with the hypo solution.

It is a further object of the invention to provide a method and apparatus which is light, inexpensive and portable.

These and other objects of the invention will be more clearly understood from the following description and the accompanying drawings, in which:

Figure 1 is a perspective view of one embodiment of my apparatus;

Figure 2 shows another embodiment of my apparatus which includes two rotating cathode elements;

Figure 3 is a top View of the apparatus of Figure l; and

Figure 4 is a side elevational view of the apparatus of Figure 1.

Referring to Figure l, a base plate 11 serves to mount the motor 12 which is connected to speed reduction gear box 13. The rotating cathode element 14 is connected to the shaft 16 of the gear box 13. The motor 12 supports the gear box 13 and the cathode 14. Anodes 17 extend through the plate 11 and are interconnected by the conductive strap 18. The base plate 11 is constructed to lit over the top of the hypo tank 21 which contains the hypo solution 22. The blocks 23 which are attached to the base plate 11 serve to prevent the base plate from slipping. The base plate may be made of any suitable material which will not be attacked by the hypo solution and which insulates the cathode and anode elements from one another. In one particular instance, the base plate was made of Lucite which lpermitted viewing the associated elements and -still gave the desired strength and insulation for supporting the associated apparatus.

With the base plate placed on top of the hypo tank, the cathode and anode elements extend down into the hypo solution. The construction of the cathode will be presently described. The anode plates 17 may be made of any suitable material which is not attacked by the hypo solution and which has a reasonably high electrical conductivity. For example, the anodes 17 may be made of carbon.

Suitable means are provided for applying a D.C voltage between the cathode and anode elements to thereby carry out the electrolytic process. We have shown D.C. power supply means 24 which comprises a rectier unit, together with voltage control means 26 and meter means 27, for observing the current which ows between the cathode and anode elements. It is to be understood, of course, that other means may be provided for obtaining a D.C. voltage across the anode and cathode; for example, battery means may be used.

Referring to Figure 3, we have vshown a top view of theapparatus of Figure 1 which shows the base plate 11, the anode elements 17 extending to the top of the base plate. The bolts 28 and 29 serve to connect the strap 1S to the two anode elements. Referring to Figure 4, wherein a side elevational view of the apparatus of Figure l is shown, the motor 12 is mounted on the base plate 11 by means of bolts 'at 31'.v The shaft 16 which extends from the gear box 13 is attached to the shaft 32 of the cathode element by the sleeve 33 which is provided with screw means 34. A sleeve 36 is secured to one end of the shaft 32 by means of screw 37. A plurality of circular cathode plates 41 are provided with a hole for accommodating the shaft 32. The plates 41 are spaced along the shaft 32 by means of spacers 42 which are preferably made of material which has a high conductivity. The other end of the shaft 32 is threaded at 43 to receive the nut 44. Thus, a series of plates 41 and spacers 42 are placed on the shaft and the nut 44 is tightened. In this manner, the plates are accurately spaced, one from the other and good electrical Contact between the shaft 32 and the plates 41 results. Thus it is seen that We have provided a cathode which is made up of a plurality of plates 41 which are easily removed from the shaft 32. The importance of this arrangement will be presently described. The plates 41 may be made of any suitable metal which will not be attacked by the hypo solution and to which the silver will readily adhere. We have found that type 316 stainless steel a common alloy, meets these requirements.

' Operation of my apparatus is as follows: The anodes 17 and cathodes 14 are submerged in the hypo solution 22. The cathode is lowered into the solution until all of the plates 41 are submerged. A D.C. voltage is applied between the cathode and anodes. The motor is energized to thereby rotate the cathode shaft and cathode plates in the hypo solution. Rotation of the plates, which are circular and smooth, causes the hypo solution to undergo a shearing action with respect to the faces of the plates. This action is such that there is always available at the surface of the plate suliicient thiosulfate ions to permit appropriate plating of the silver without formation of silver sulfide. 'I'his is in great part due to the fact that the plates do not have any abrupt surfaces which contact the liquid and agitate the liquid to form dead spaces or pockets where there is no thiosulfate ion present. If the plates were a different shape or if the plates were not smooth, then the liquid could be agitated and dead spaces or pockets would be formed. The action of the rotating plates 41 tends to set up a slow circulating current in the tank whereby fresh solution passes across the plates. Thus it is seen that we have provided a means whereby a sufficient supply of thiosulfate ions is present adjacent the plates at all times. No dead spaces or pockets exist where silver sulfide might be formed.

We have further found that the plating current (plating rate) may be increased by increasing the speed of rotation of the cathode without forming silver sulfide.

Whenever it is desired to clean the cathode plates, the

nut 44 is removed and the various plates are dismounted from the shaft 32. The plates are then slightly bent to break away the silver which has been plated on their surface. This is easily accomplished since the surface of the plates is smooth and the silver does not tightly adhere to this surface. When the various plates have been cleaned, they are reassembled on the shaft 32. it has been found that this apparatus greatly increases the rate of allowable current which can Aiiow between the anodes and plates without the formation of a silver sulfide. The life of solutions has been prolonged as much as ten times when an apparatus of this type has been employed.

in Figure 2, we have shown apparatus ofthe type described above which comprises a motor 51 which is connected to two reduction gear boxes 52 and S3. The cathode elements 54 and 55 of the type previously described are connected to the gear reduction box. Anode elements 57 and 58 which are similar to the elements 17 already described are placed in the solution adjacent the cathode element 54. As before, a voltage is applied between the cathode and anode elements and the cathode element is rotated when the current is applied to prevent formation of sulfide. The arrangement shown in Figure 2 has the advantage that the rate at which the silver is removed from the hypo solution is approximately double the rate of the single unit shown in Figure l. in certain applications, for example where a large hypo solution tank is employed, it is advantageous to employ equipment of this type.

Thus it is seen that we have provided apparatus for prolonging the life of hypo solutions which is easy to operate and portable. The apparatus as described has the advantage tha no dead spaces or pockets exist where silver sulde might be formed. The plating rate may be increased by increasing the speed of rotation of the cathode and the plating current. Further, the only movable part which is in contact with the Solution is the cathode element, and no problem of wear or corrosion of bearings or pumps exists. The cathode elements are easily removed for removal of the silver and are easily reinserted on the cathode shaft. It is apparent that the apparatus described above has many advantages over existing apparatus.

We claim:

l. In apparatus for rejuvenating and prolonging the life of hypo solutions, a shaft adapted to extend vertically into the solution, said shaft being unsupported at its lower end, a plurality of spacers, a plurality of flat circular members mounted on said shaft with their principal plane perpendicular to the axis of said shaft and separated from each other by said spacers, said shaft, spacers, and members forming a cathode element, at least one elongated anode member adapted to extend vertically into the solution and adjacent the peripheral edge of said circular members, means for applying a D.C. voltage between said anode member and said cathode element, and means for driving said shaft to thereby rotate said cathode element.

2. Apparatus as in claim l wherein said driving means includes means for driving said cathode element at a speed which corresponds to a given applied voltage.

3. In an apparatus for rejuvenating and prolonging the life of hypo solutions, a shaft adapted to extend vertically into the solution, said shaft being unsupported at its lower end, a plurality of flat circular members mounted on said shaft with their principal plane perpendicular to the axis of the shaft and equally spaced from each other, said shaft and members forming a cathode element, at least one elongated anode member adapted to extend vertically into the solution and adjacent the peripheral edge of said circular members, means for applying a D.C. voltage between said anode member and said cathode element, and means for driving said shaft to thereby rotate said cathode element causing a shearing action between said circular members and the solution.

4. In apparatus for rejuvenating and prolonging the life of hypo solutions, a shaft adapted to extend vertically into the solution, said shaft being unsupported at its lower end, a plurality of spacers, a plurality of fiat circular members mounted on said shaft with their plane perpendicular to the axis of said shaft and separated from each other by said spacers, whereby said spacers provide means for spacing said members and form a competent electrical connection between said shaft and said members, said shaft, spacers and members forming a cathode element, at least one elongated anode member adapted to extend vertically into said solution and adjacent the peripheral edge of said circular members, means for applying a D.C. voltage between Isaid anode member and said cathode element, speed reduction means connected to said shaft, means for driving said shaft through said reduction means,

said driving means serving to support said cathode element and speed reduction means, and means for mounting said driving means and said anodes, said mounting means also providing means for mounting the apparatus on the hypo tank.

5. In apparatus for use in hypo baths to rejuvenate and prolong the life of the hypo solution, a shaft adapted to extend vertically into the solution, said shaft being unsupported at its lower end, a plurality of spaced at circular members mounted on said shaft with their principal 10 plane perpendicular to the axis thereof, said circular members forming a cathode element, at least one elongated anode member adapted to extend into the solution adjacent the peripheral members, means for applying a D.C.

voltage between said anode and cathode element, means for driving said shaft, said driving means serving to support said cathode element, and means serving to mount said driving means and said anode, said mounting means being adapted to removably mount the apparatus on the hypo bath.

References Cited in the file of this patent UNITED STATES PATENTS 526,482 Bridgman Sept. 25, 1894 1,181,077 Holden Apr. 25, 1916 1,954,316 Hickman et al Apr. 10, 1934 2,255,429 Lyons Sept. 9, 1941 

1. IN APPARATUS FOR REJUVENATING AND PROLONGING THE LIFE OF HYPO SOLUTIONS, A SHAFT ADAPTED TO EXTEND VERTICALLY INTO THE SOLUTION, SAID SHAFT BEING UNSUPPORTED AS ITS LOWER END A PLURALITY OF SPACERS, A PLURALITY OF FLAT CIRCULAR MEMBERS MOUNTED ON SAID SHAFT WITH THEIR PRINCIPAL PLANE PERPENDICULAR TO THE AXIS OF SAID SHAFT AND SEPARATED FROM EACH OTHER BY SAID SPACERS, SAID SHAF, SPACERS, AND MEMBERS FORMING A CATHODE ELEMENT, AT LEAST ONE ELONGATED ANODE MEMBER ADAPTED TO EXTEND VERTICALLY INTO THE SOLUTION AND ADJACENT THE PERIPHERAL EDGE OF SAID CIRCULAR MEMBERS, MEANS FOR APPLYING A D-C. VOLTAGE BETWEN SAID ANODE MEMBER AND SAID CATHODE ELEMENT, AND MEANS FOR DRIVING SAID SHAFT TO THEREBY ROTATE SAID CATHODE ELEMENT. 